Motor vehicles with rotating drive shafts create in different situations unwanted drivetrain vibrations. The cause is often, during the start of a motor vehicle, the start clutch between the combustion engine and the transmission of the vehicle, due to the friction characteristics or due to geometric inconsistencies of its friction lining. Also, uncomfortable vibrations can occur in electrically driven vehicles through the operation of the electric machine. Thus, drive train vibrations can be brought into the drive train through the drive wheels, for instance when driving through a pothole or a manhole cover. Drive train vibrations, depending on the amplitude and frequency, are felt by the passengers in the vehicle as being unpleasant.
The drive train vibrations can be influenced by suitable adjustment means, for instance at the starting clutch, at the combustion engine, or at the electric machine, so that they are largely dampened or in the ideal case completely suppressed.
A method for the suppression of vibrations in the drive train is described in DE 40 09 791 A1 for a motor vehicle which is driven by a combustion engine whereby, when vibrations in the drive train occur, the combustion engine receives a manipulated variable which alters the drive torque of the combustion engine. To recognize such vibrations and to dampen them fast and effectively, it is proposed to determine, through rotational speed information, the rotational speed gradients and using them to determine the vibration and that, by means of a proper phase shift of the first ignition time points in an ignition time point control device, the stored ignition diagram is modified in the respective ignition time points of a second ignition time point control device, and the drive torque of the combustion engine is modified in a way that the vibration and the drive train of the combustion engine are dampened.
DE 10 2011 115 927 A1 teaches a method for the recognition of rotational speed/torque variations, in particular of samples of such deviation of a drive device in a motor vehicle, the method having the following steps: recognition of a critical rotational speed situation, in particular by means comparisng a measured actual rotational speed with predetermined given rotational speed, retrieval of a local rotational speed minimum and a local rotational speed maximum (local rotational speed parameters), evaluation of these local rotational speed parameters, in particular the creation of local rotational speed parameter values, like preferably of a local amplitude and a local frequency, a direct or indirect determination of the duration of a local vibration time interval, whereby in particular within this time interval constant local rotational speed parameters are present, and the description of a local vibration sample which possesses at least the local amplitude, the local frequency, or the local vibration interval.
Another method for the reduction of vibrations in a motor vehicle is described in DE 102 44 026 A1. In this method, interfering vibrations are recognized by a control and regulation device by means of proper send source and, during exceeding prior determined limiting values, at least one device is actuated in a way that the interfering vibration is completely eliminated or at least dampened in its amplitude. Wherein, the at least the one device acts on an at least one rotating part in the vehicle drive train in such a manner that the latter, when a vibration occurs, is continuously or periodically slowed down in its rotational motion or is actuated to compensate for vibration. Hereby, the compensation vibration or the brake action has the same or a similar frequency as the interfering vibration but it has, however, a vibration phase shift with it which creates a reduction of the amplitude of the interfering vibration.
A weak point in these publications and the taught method arises because recognition of these vibrations requires additional sensors, for instance torque sensors, and/or the typical sensor information which is present, is analyzed unfavorably. Often, computation intensive algorithms are applied to analyze the amplitude and phase position of the drive train vibration. If, like it is in many occasions, a rotational speed signal or a differential rotational speed signal that is used as the basis for the vibration damping, the disadvantage is that hereby a phase delay is created which demands larger requirements in regard to the so-called cut-off frequencies, and which are difficult to meet. In practice, it is often the case that the signal for the damping of the vibration is not simultaneous with the interfering vibration, but is issued after a delay of one period.